Question

I am writing a DSL for expressing flow (original I know) in groovy. I would like to provide the user the ability to write functions that are stored and evaluated at certain points in the flow. Something like:

states {
    "checkedState" {
        onEnter {state->
           //do some groovy things with state object
        }
    }
}

Now, I am pretty sure I could surround the closure in quotes and store that. But I would like to keep syntax highlighting and content assist if possible when editing these DSLs. I realize that the closure COULD reference artifacts from the surrounding flow definition which would no longer be valid when executing the closure in a different context, and I am fine with this. In reality I would like to use the closure syntax for a non-closure function definition.

tl;dr; I need to get the closure’s code while evaluating the DSL so that it can be stored in the database and executed by a script host later.

Answer 1

I don’t think there is a way to get a closure’s source code, as this information is discarded during compilation. Perhaps you could try writing an AST transformation that would make closure’s syntax tree available at runtime.

If all you care about is storing the closure in the database, and you don’t need later access to the source code, you can try serializing it and storing the serialized form.

Closure implements Serializable, and after nulling its owner, thisObject and delegate attributes I was able to serialize it, but I’m getting ClassNotFoundException on deserialization.

def myClosure = {a, b -> a + b}

Closure.metaClass.setAttribute(myClosure, "owner", null)
Closure.metaClass.setAttribute(myClosure, "thisObject", null)
myClosure.delegate = null

def byteOS = new ByteArrayOutputStream()
new ObjectOutputStream(byteOS).writeObject(myClosure)
def serializedClosure = byteOS.toByteArray()

def input = new ObjectInputStream(new ByteArrayInputStream(serializedClosure))
def deserializedClosure = input.readObject() // throws CNFE

After some searching, I found Groovy Remote Control, a library created specifically to enable serializing closures and executing them later, possibly on a remote machine. Give it a try, maybe that’s what you need.